The present invention relates generally to a vehicle seat assembly and, more particularly, to a plastic framework for the seat back having an adjustable head-rest support. The present invention also relates to a method for manufacturing the plastic framework for the seat back.
It is a recent trend in the automobile industry to minimize the weight of an automobile and, for this purpose, a synthetic resin or plastics is largely employed as material for various component parts of automobile interior installations. An automobile seat assembly including a seat and a seat back is not an exception, such as disclosed in the Japanese Laid-open Patent Publication No. 54-155526, laid open to public inspection on Dec. 7, 1979.
The use of the synthetic resin is effective not only to reduce the weight of the automobile seat assembly, but also to enable the automobile seat assembly to be manufactured in one-piece construction by means of the existing plastics molding technique. However, it has been found that the structure of a framework for the seat assembly which can be manufactured in one-piece construction by the utilization of the existing plastics molding technique is limitted and, in particular, a difficulty is involved in the manufacture of the automobile seat framework of a type having some working elements.
When it comes to a head rest assembly for supporting and protecting the head of an occupant sitting on the automobile seat assembly, a support for the support of the head rest assembly requires a relatively high rigidity sufficient to make the head rest assembly withstand against impacts the occupant's head may give thereto during, for example, automobile collision. Because of the design limitation imposed on the plastics molding technique and also because of the relatively high rigidity required by the head rest support, the head rest assembly combined in the head rest assembly is such that the height of the head rest relative to the seat back cannot be adjustable. In other words, according to the prior art, the conventional seat back framework made of plastics is molded together with the head rest and has no capability of adjusting the height of the head rest relative to the seat back according to the occupant's sitting height.